The incorporation of small bubbles of air or other gas into the boundary layer water next to a boat hull, in order to reduce hull drag, is not new; small and medium size boats have been designed with this feature for several years. These boats are designed to capture air at the bow and to force it to mix with and be entrained by the water next to the hull; this air-water mixture then alters the boundary layer which envelopes the hull. Since the viscosity of the air-water mixture is lower than that of water alone, the friction drag on the hull is reduced.
This method of getting air into the boundary layer is adequate for small boats; for larger hulls it presents several problems. First, larger hulls are usually made of steel, which presents fabrication problems due to the somewhat more complex hull shapes required for air entrainment. Second, it is sometimes difficult to get air to remain entrained within the boundary layer for the entire length of a long hull, since the hull tends to cause the water beneath it to be forced out to the sides of the hull. The result of these two phenomena is that the boundary layer along the aft part of the hull has little or no air within it, and consequently there is no reduction in drag along this portion of the hull.
Injecting air through small holes in the hull would not be practical, since these small holes would be subject to clogging by mud and/or marine organisms. Furthermore, unless the holes were extremely small, the bubbles could increase instead of decrease the drag; this is so because the bubbles would then generate additional drag at their points of production due to their size, rather than being assimilated into the boundary layer.